The instant invention relates to a belt feeder for feeding sheets of paper from an upstream supply to downstream apparatus and further processing. More particularly, the invention relates to the pulleys used with the feeding belts which assure that the sheets of paper are advanced without the introduction of skew to the advancing paper.
Mechanisms for the feeding of paper documents generally fall into two categories, those being vacuum fed and friction fed. The following description of the prior art will deal only with those types of feeders an material handlers which are considered to be friction-type feeders and which include singulators.
Friction feeders are preferred when it comes to feeding single paper documents. Friction feeders, as the name implies, rely on the interaction of several components that result in the singulation of paper documents. Two methods of singulation are provided by friction feeders. One style is via top feed and the second style is via bottom feed. A friction feeder is designed to operate as a top feed or a bottom feed, but it cannot operate in both modes. The components are usually a drive roller and a retarding device. The retarding device is of a material which provides a high coefficient of friction between the paper being fed and the drive roller.
In a bottom feed configuration, the paper begins as a vertical stack placed on a plurality of belts which usually are supported by a feeder table. This plurality of belts then advance the stack of paper toward a retarding device. As the plurality of belts advance the stack of paper under the retarding device, the friction between the belts and the bottom of the stack of paper tends to pull paper off the bottom of the stack. The retarding device provides the friction that acts to hold back the stack of paper. Therefore, the number of paper documents that are pulled from the bottom of the vertical stack is determined by the physical distance between the belts and the retarding device. If the distance is substantially the thickness of a single piece of paper, or the thickness of the material being singulated, a single paper will be delivered from the bottom of the stack. The single sheet delivery is generally the desired result. If the distance between the belts and the retarding device is the thickness of several pieces of paper or of the documents to be singulated, then a stream of paper documents will be delivered from the stack.
Typical singulating feeders employ two timing belts each of which rides on two or more timing pulleys which are removably secured (typically by screws) to shafts which rotate and drive the belts. The shafts include a flat to receive a set screw through the pulley. Unfortunately, when such a singulating feeder is first started, there is usually some slippage, however minute, between the pulley and the shaft, which results in one belt fitting on its pulleys differently than the other belt fits on its pulleys. Typically, the teeth of one belt will fit on its supporting pulleys in such a way that the belt will not be driven by the pulleys, but rather is being pulled along, resulting in excess wear and tear on the other belt, which winds up being the only belt to be positively driven. Also, one belt will tend to become angled with respect to the other belt, and this lack of parallel belts will introduce skew to the documents being fed by the belts. Such arrangements allow for the documents being fed by the belts to become skewed prior to their contacting the separator stone which means the documents emerge from the separator stone skewed, which causes problems with downstream processing of the documents. Accordingly, the instant invention provides apparatus which maintains the timing belts parallel and properly seated on the pulleys at the start of operation and eliminates skew from a singulating feeder and assures that the documents exiting the singulator emerge without any skew.